A little over a year after Andrew Formica and Dick Weilteamed up to lead the freshly merged Janus Henderson [profile] as co-CEOs, a single chief is taking over. And another top executive is leaving, too.

Today the London-based multinational asset manager's board of directors confirmed the appointment of Weil as the sole CEO. Formica will step down as co-CEO and from the Janus Henderson board will stay on through the end of the year to advise on the final integration efforts, and the firm will take a $12-million severance charge.

Richard Gillingwater, chairman of the board, praises Weil as bringing "a breadth of skills and experience from prior roles in his career where he successfully led organizations through challenge and change."

Meanwhile, global distribution chief Phil Wagstaff (like Formica, a Henderson alumnus) is also leaving Janus Henderson, the board confirms. He will stay on for six months to help with the transition.&nbsp